Torque split hydraulic coupling between transmission and secondary driving axle with torque modulation and locking capabilities

ABSTRACT

A power transmission system coupling ( 100 ) configured to provide a responsive and controllable clutch ( 110 ) using a torque split arrangement including a planetary gear set ( 106 ) for torque modulation, together with a locking device ( 134 ) to maximize torque transfer capability when modulation is not required.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to, and claims priority from U.S.Provisional Patent Application No. 60/400,383 filed on Jul. 31, 2002,and is related to, and claims priority from U.S. Provisional PatentApplication No. 60/401,111 filed on Aug. 5, 2002.

TECHNICAL FIELD

The present invention relates generally to vehicle power transmissionsystems coupled between a driving motor and one or more driven vehiclewheels, and in particular, to a power transmission system torquecoupling configured to provide a responsive and controllable clutchusing a torque split arrangement including a planetary gear set fortorque modulation, together with a locking device to maximize torquetransfer capability when modulation is not required.

BACKGROUND ART

Most light automotive vehicles, such as automobiles, sport-utilityvehicles, vans and light trucks, have four wheels, but in the typicalvehicle the driving engine which propels the vehicle is coupled to onlytwo of the wheels. In older vehicles the rear wheels normally propelledthe vehicle, but in newer vehicles it is commonly the front wheels.Light trucks and off-road vehicles commonly have four-wheel drive (4WD),the famous U.S. Army Jeep for example, but often operate with powerdelivered to only two wheels. If the need arises for more traction, thetransmission output is coupled with the other two wheels through amanually operated transfer case. The rear and front wheels share thetorque delivered by the driving engine under a fixed gear ratio.

In recent years automotive manufacturers have produced moresophisticated vehicles with all wheel drive (AWD). In the typicalvehicle of this type, all four wheels normally drive the vehicle withthe engine torque split between the front and rear wheels. The drivingengine delivers power through a transmission which is in turn connecteddirectly to two of the wheels, referred to as the primary drivingwheels. The remaining two wheels, referred to as the secondary drivingwheels, are connected to the transmission through a torque couplingwhich accommodates slight variations in speed between the primary andsecondary wheels.

While a differential is commonly interposed between the primary drivingwheels and the transmission, the connection is considered “direct” inthe sense that no slippage can develop between the primary wheels andthe transmission. While a second differential is commonly interposedbetween the torque coupling and the secondary wheels, the connection is“indirect” as the torque coupling allows for slippage between thesecondary wheels and the transmission. The torque coupling operates todivides the torque between the primary and secondary wheels.

Torque couplings are used in four-wheel-drive or all-wheel-driveapplications to transfer torque to the secondary axle or to provide alimited slip differential function between a pair of wheels on a singleaxle under operating conditions where one wheel on the axle loosestraction. An essential characteristic of a torque coupling is thecapability of modulating the torque delivered by the driving engine, inorder to improve vehicle handling, safety, and acceleration performance,even under no-wheel-slip conditions and at higher vehicle speeds. Thereare basically two functions to be performed by a torque coupling in afour-wheel or all-wheel drive application. First, traction enhancementsat low speed and high torque operating conditions, and second, vehicledynamic control at high speed and low torque operating conditions.

One type of torque coupling is a hydraulic coupling. Hydraulic couplingsconsist essentially of a wet-plate clutch and a pumping mechanismsupplying pressure required for the clutch actuation.

Usually, as is shown in U.S. Pat. No. 5,595,214 to Shaffer et al., andin U.S. Pat. No. 5,469,950 to Lundström et al., the pumping mechanism isof the gerotor or geared pump type, or the piston/axial cam type, and isconfigured to take advantage of the differential speed resulting fromslip between either a pair of axles of the vehicle, or between eachwheel on a common axle, to provide the pressure to actuate the clutch.

The overall coupling responsiveness depends upon the speed with whichthe hydraulic pressure is created and how rapidly the pressure can beapplied to the clutch. As is well known, the hydraulic fluid volume flowachieved by the pumping mechanism and the directly proportionalhydraulic fluid pressure differential each depend on the relative speedbetween the pumping mechanism components.

Accordingly, it would be desirable to provide a coupling device, such asa hydraulic coupling, with improved responsiveness for torquemodulation, and which is capable of maximizing torque transfer from thedrive motor to the driven components when torque modulation is notrequired.

SUMMARY OF THE INVENTION

Briefly stated, a torque coupling of the present invention includes aclutch and a planetary set connected such that two torque-transfer pathsexist through the coupling, a mechanical path and a clutch path. Animproved responsive and controllable clutch in the clutch pathaccommodates slippage in the torque coupling and controls the amount oftorque transferred in each of the paths. A locking device in the clutchpath is configured to maximize the torque transfer capability throughthe mechanical path of the torque coupling when torque modulationthrough the clutch path is not required. The proportion of torquetransmitted through the mechanical path in comparison to the torquetransmitted through the clutch path is determined by the design of theplanetary set and the associated planetary gear ratios.

In an additional embodiment of the present invention, the torquecoupling is a hydraulic torque coupling and is further configured with apumping mechanism and a wet plate clutch.

In an additional embodiment of the present invention, the torquecoupling is a hydraulic torque coupling and is further configured with agear pump and a wet plate clutch.

In an additional embodiment of the present invention, the torquecoupling is a hydraulic torque coupling and is further configured with apiston pump and a wet plate clutch.

The foregoing and other objects, features, and advantages of theinvention as well as presently preferred embodiments thereof will becomemore apparent from the reading of the following description inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a schematic view of a front wheel drive automobile providedwith a torque coupling constructed in accordance with and embodying thepresent invention;

FIG. 2 is a schematic view of a rear wheel drive automobile providedwith the torque coupling;

FIG. 3 is a simplified sectional view of a hydraulic torque coupling ofthe present invention configured with a pumping mechanism;

FIG. 4 is a simplified sectional view of an alternate embodimenthydraulic torque coupling of the present invention configured with agear pump;

FIG. 5 is a simplified sectional view of an alternate embodimenthydraulic torque coupling of the present invention configured with apiston pump;

FIG. 6 is a simplified sectional view of a torque coupling of thepresent invention configured with a locking device disposed between thesun gear and ring gear;

FIG. 7 is a simplified sectional view similar to FIG. 6 with analternate configuration locking device disposed between the sun gear andring gear;

FIG. 8 is a simplified sectional view of a torque coupling of thepresent invention configured with a locking device disposed between theplanet carrier and ring gear;

FIG. 9 is a simplified sectional view of a torque coupling of thepresent invention configured with a locking device disposed between thesun gear and planet carrier; and

FIG. 10 is a plot of torque versus vehicle speed for a variety ofvehicle operating conditions and configurations.

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the invention, describes severalembodiments, adaptations, variations, alternatives, and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention.

Turning to FIG. 1, an automotive vehicle, such as a passenger car, asports utility vehicle, a van or even a truck, is shown at 10, andincludes a pair of primary driving wheels 12, which are the front roadwheels, and pair of secondary driving wheels 14, which are the rear roadwheels. A driving engine 16 is provided which is either transversely orlongitudinally mounted, and is coupled to a transmission 18 which may beof the automatic type or manual type. The driving engine 16 andtransmission 18 constitute a power unit that delivers torque through atransmission output shaft 20, such as the main shaft of the transmission18. The output shaft 20 of the transmission 18 is connected to theprimary driving wheels 12 through a primary differential 22. Theconnection is direct in the sense that no slippage occurs between theoutput shaft 20 and the primary wheels 12.

The output shaft 20 of the transmission 18 is also connected to thesecondary driving wheels 14 through a torque coupling 100 of the presentinvention and a secondary differential 24, but the connection isindirect, inasmuch as the torque coupling 100 accords a measure ofslippage between the secondary wheels 14 and the transmission shaft 20and likewise between the secondary wheels 14 and the primary wheels 12.The slippage accommodates small variations in velocity between theprimary and secondary wheels 12 and 14, changes which may be occasionedby variances in tire size or by negotiating turns. Preferably the torquecoupling 100, is located at or close to the primary differential 22 andis connected to the output shaft 20 of the transmission 18 through adrive shaft 26 which extends longitudinally through the vehicle 10.

Turing to FIG. 2, an alternate automotive vehicle 30 is shown withessentially the same components as the vehicle 10, except that they areorganized differently. In vehicle 30 the primary driving wheels 12 andprimary differential 22 are at the rear of the vehicle, whereas thesecondary driving wheels 14 and the secondary differential 24 are at thefront of the vehicle. The driving engine 16 and transmission 18, whilebeing at the front of vehicle 30, are mounted longitudinally. The outputshaft 20 of the transmission 18 and the primary differential 22 areconnected through a primary drive shaft 28. The torque coupling 100 isconnected to the transmission output shaft 20 through a chain 31, andthe torque coupling 100 is, in turn, connected to the secondarydifferential 24 through a secondary drive shaft 32.

Each vehicle 10, 30 possesses a variety of sensors which produceelectrical signals that reflect the conditions under which the vehicleoperates, and those signals are fed to an onboard microprocessor whichevaluates them and produces a signal that controls the torque coupling100. The torque coupling 100 is responsive to the signals to apportionthe torque delivered at the output shaft 20 of the transmission 18between the primary driving wheels 12 and the secondary driving wheels14 to enable the vehicle to best respond to the driving conditionsmonitored by the sensors. Among the driving conditions monitored may beangular velocity of each of the wheels 12 and 14, longitudinalacceleration, lateral acceleration, torque delivered at the output shaft20 of the transmission 18, position of the throttle for the drivingengine 16, and position of the steering gear (steering angle).

The torque coupling 100 apportions the torque delivered at thetransmission 18 between the primary driving wheels 12 and the secondarydriving wheels 14 to best satisfy the conditions under which the vehicleoperates at the time. As shown in FIG. 3, the torque coupling 100includes an input member or shaft 102 connected to the shaft 20 of thetransmission 18, and an output member or shaft 104 connected to thesecondary differential 24. The two shafts 102 and 104 rotate about acommon axis X. The torque coupling 100 further includes a planetary gearset 106 contained within a housing 108, and which is organized about theaxis X. An optional output gear 109 is coupled directly to the housing108, co-axial with the output shaft 104, to provide a second output pathfor the torque coupling 100. The planetary gear set 106 is connected toboth the input and output shafts 102 and 104. Finally, the torquecoupling 100 includes a clutch 110 that is also located around the axisX, adjacent the input shaft 102 to the planetary gear set 106, such thattorque is transferred between the input shaft 102 and planetary gear set106 with slippage.

The torque coupling 100 provides two torque transfer paths between theinput shaft 102 and the output shaft 104. The first torque transfer pathis a purely mechanical path that passes from the input shaft 102, to thehousing 108, and through the planetary gear set 106 to the output shaft104.

The second torque transfer path is a clutch path which passes from theinput shaft 102, through the clutch 110 and the planetary gear set 106,to the output shaft 104. The majority of the transmitted torque passesthrough the torque coupling 100 over the mechanical path, which isreferred to as the high torque path. The clutch path functions as thelow torque path.

The planetary gear set 106 includes a sun gear 112 having a stub shaft114 extended from it into the clutch 110. It also includes a ring gear116 to which the input shaft 102 is coupled through the housing 108. Aportion of the housing 108 is coupled to the input shaft 102, and isdisposed in operative relationship with the ring gear 116. In addition,the planetary gear set 106 has planet gears 118 that are located betweenthe sun gear 112 and ring gear 116 and engage both. Finally, theplanetary gear set 106 has a carrier 120 provided with spindles 122 onwhich the planet gears 118 rotate. The carrier 120 is connected directlyto the output shaft 104. The gears 112, 116, and 118 together with thecarrier 120 constitute elements of the planetary set 106.

In the operation of the vehicle, the driving engine 16 generates torquewhich is transferred through transmission 18, which has the capacity toalter the torque, so that the torque delivered at the shaft 20 of thetransmission 18 may be different from that delivered by the drivingengine 16. A portion of the torque at the transmission shaft 20 isdelivered to the primary driving wheels 12 through the primarydifferential 20 without any slippage between the wheels 12 and thetransmission shaft 20. The remaining torque is delivered to thesecondary wheels 14 with some slippage between the transmission shaft 20and the secondary wheels 14, and that slippage occurs within the torquecoupling 100. The total amount of torque delivered at the primary wheels12 and at the secondary wheels 14 approximately equals the torque in theshaft 20 of the transmission 18, with some losses due to frictionbetween the components.

However, the apportionment of that torque between the primary wheels 12and the secondary wheels 14 may not be equal, and under most drivingconditions is not. The apportionment of torque between the primarywheels 12 and the secondary wheels 14 is dependent on the clutch 110 ofthe torque coupling 100.

The shaft 20 of the transmission 18, coupled to the input shaft 102 ofthe torque coupling 100, rotates the input shaft 102 and transferstorque to the input shaft 102. Within the torque coupling 100, thetorque splits into two paths and then recombines, so that the torque inthe output shaft 104 of the torque coupling 100 essentially equals thetorque in the input shaft 102, at least when minimum slippage occurs inthe clutch 110. In one path, the mechanical path, the torque passes fromthe input shaft 102 to the housing 108, and on to the ring gear 116 ofthe planetary gear set 106. From the ring gear 116, the torque is passedthrough the planet gears 118 to the planet carrier 120, and finally tothe output shaft 104. For the other path, the clutch path, the torquepasses from the input shaft 102 to the clutch 110, then to the sun gear112 of the planetary set 106 through its stub shaft 114. From the sungear 112, the torque is passed to the planet gears 118 and finallythrough the carrier 120 to the output shaft 104. The hookups between theplanetary gear set 106 and the clutch 110 are such that the mechanicalpath transfers more torque than the clutch path.

The division of torque between the two paths depends on the gear ratio Ubetween the ring gear 116 and the sun gear 112, which is a function ofthe number of teeth on the ring gear 116 versus the number of teeth onthe sun gear 112. The higher the ratio U, the less the amount of torquetransferred through the clutch path and conversely the more torquetransferred through the mechanical path. Preferably, most of the torquetransferred through the torque coupling 100 passes through themechanical path and relatively little through the clutch path, therebypermitting a downsizing of the clutch 110.

A reduction of force exerted on clutch 110 will reduce the torquetransmitted through the clutch path, and that in turn will reduce thetotal torque delivered through the output shaft 104 to the secondarywheels 14. Since the torque in the output shaft 104 generally equals thetorque in the input shaft 102, a lesser amount of torque is divertedfrom the shaft 20 of the transmission 18 to the input shaft 102 of thetorque coupling 100, leaving a greater amount to be transferred to theprimary driving wheels 12. Conversely, when the force exerted on theclutch 110 increases, the clutch 110 transfers more torque whichtranslates in more torque in the clutch path and a proportionallygreater torque at the output shaft 104, and at the input shaft 102 aswell. The greater demand for torque by the input shaft 102 leaves lesstorque for the primary drive wheels 12. Thus, the amount of forceapplied to the clutch 110 determines the proportion of the total torqueat the transmission shaft 20 which is diverted through the torquecoupling 100 and that is of course the amount of torque delivered to thesecondary wheels 14. The remaining torque from the transmission shaft 20goes to the primary wheels 12.

In short, the force applied to the clutch 110 controls the division oftorque between primary wheels 12 and the secondary wheels 14, and thatforce, together with the amount of slippage in the clutch 110 and othervariables, such as temperature, controls the amount of torquetransferred through the clutch 110. The clutch 110 experiences someslippage under typical driving conditions, with the input shaft 102rotating slightly faster than the output shaft 104, but the differencein angular velocities is not substantial and produces only a very smalldissipation of power.

As shown in FIG. 3, clutch 110 preferably is a wet plate clutch actuatedby a conventional pumping mechanism 124 contained within the housing 108of the torque coupling 100. The pumping mechanism 124 is configured totake advantage of the differential speed resulting under slip betweenthe two axles of the vehicle 10, 30 or between the two wheels on asingle axle, to provide pressure to actuate the clutch 110. The volumeflow of hydraulic fluid achieved by the pumping mechanism 124 and thedirectly proportional pressure differentials are dependant upon therelative speed between the pump members. In the torque coupling 100, therelative speed between the pump member is equal to the relative speedbetween the sun gear 112 and the ring gear 116 in the planetary set 106.This relative speed is further dependant upon the planetary gear ration,and is a multiple of the relative speed between the input shaft 102 andthe output shaft 104. Hence, the planetary set 106 provides anamplification effect on the speed between the pump members, which isbeneficial for the volume flow and pressure delivered by the pumpmechanism 124, thereby reducing the clutch torque requirements.

In one embodiment, shown in FIG. 4, the pumping members of the pumpmechanism 124 consist of an internal gear 126 and an eccentricallymounted external gear 128. Rotation of the external gear 128 about theX-X axis on the eccentric mounting provides a pumping force for thehydraulic fluid and engagement of the clutch 110.

In a second embodiment, shown in FIG. 5, the pumping members of the pumpmechanism 124 consists of an axial cam plate or swash plate 130connected to the sun gear 112, and a piston pump 132 disposed in a pumphousing 134, connected to the torque coupling housing 108. The axial camplate or swash plate 130 has a variable thickness around thecircumference, and imparts a reciprocating motion parallel to the axisX-X on the piston pump 132 during rotation about the axis X-X. Thepiston pump 132 provides a pumping force for the hydraulic fluid andengagement of the clutch 110.

Turning to FIGS. 6 through 9, a locking mechanism 134 is shown disposedwithin the torque coupling housing 108. The locking mechanism 134 isconfigured to maximize the torque transferred between the input shaft102 and the output shaft 104 of the torque coupling 100 when the clutch110 is not being utilized to modulate the torque transfercharacteristics.

The locking mechanism 134 may be placed in parallel with the torquemodulation clutch 110, as shown in FIGS. 6 and 7. In FIG. 6, the lockingmechanism consists of a roller, sprag, or strut controlledbi-directional clutch 136 disposed between the sun gear 112 and thetorque coupling housing 108 upon which the ring gear 116 is fixed. Asshown in FIG. 6, the bi-directional clutch 136 may be disposed tooperate radially from the axis X-X, or, as shown in FIG. 7, thebi-directional clutch 136 may be disposed to operate co-axially with theaxis X-X. When the locking mechanism 134 is disposed between the sungear 112 and the ring gear 116, the locking mechanism 134 experiencestorque and speed conditions similar to the ones on the torque modulatingclutch 110. Therefore, the torque capacity requirements for the lockingmechanism 134 are significantly reduced for the same reasons as they arefor the torque modulating clutch 110. At vehicle low speed and hightorque, the torque modulating clutch 110 is disengaged, while thelocking mechanism 134 is engaged for maximum torque transfer through themechanical path. At vehicle higher speeds and lower torque, the lockingdevice is disengaged and the torque transfer is controlled exclusivelythrough the modulation of the torque modulating clutch 110.

In alternate embodiments, the locking mechanism 134 is disposed betweenother members of the planetary gear set 106. For example, as shown inFIG. 8, the locking mechanism is disposed between the torque couplinghousing 108 on which the ring gear 116 is disposed and the planetcarrier 120 of the planetary gear set 106. This configuration providesis the effective equivalent to locking the input shaft 102 with theoutput shaft 104 when the locking mechanism 134 is engaged. In a secondalternate embodiment, shown in FIG. 9, the locking mechanism 134 isdisposed between the sun gear 112 and the planet carrier 120 of theplanetary gear set 106.

Overall, the torque transmission capacity of the torque coupling 100need not be equal to the maximum torque output of the driving engine 16or transmission 18. Rather, as illustrated in FIG. 10, the torquecapacity of the torque coupling 100 may be significantly lower than themaximum torque output of the driving engine 16 or transmission 18,resulting in a lighter and less expensive construction. Different roadconditions serve to limit the maximum torque which can be delivered to adriven vehicle wheel before wheel slippage will occur. For dry pavementconditions, the maximum torque is relatively large. As logicallyexpected, the maximum amount of torque which can be delivered to adriven wheel prior to slippage decreases as the pavement becomes wet orsnow-covered. As illustrated in FIG. 10, the torque coupling 100 can beconstructed to permit a level of torque transmission to the secondarywheels 14 of a vehicle 10 which is slightly below the maximum amount oftorque expected for wet pavement conditions, thereby preventing thesecondary wheels 14 from slipping simultaneously with the primary drivenwheels 12, and enhancing vehicle traction and dynamic control.

Other variations are possible and they may employ the same planetarysets 106, pumping mechanism 124, and locking mechanism 134 withdifferent hookups or even different planetary sets. Irrespective of thehookup or planetary set, the arrangement should split the torque into amechanical path and a clutch path, with most of the torque passingthrough the mechanical path, and provide a locking mechanism 134 tomaximize torque transfer through the mechanical path when torquemodulation on the clutch path is not required. In the same vein, theinput shaft 102 and output shaft 104 may be reversed, so that torque isapplied to the output shaft 104 and delivered from the input shaft 102.Moreover, the planetary sets 106 need not rely on gearing, but insteadon friction surfaces, thus becoming traction devices or drives.

Further, the torque coupling 100 need not be confined to the transfer oftorque to the secondary wheels 14 of a vehicle, and may haveapplications in machinery other than that in automotive vehicles, andeven in automotive vehicles may be used in different locations.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results are obtained. Asvarious changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A multi-path torque coupling comprising: an input shaft adapted to beconnected to a source of torque; an output shaft from which torque isdelivered, said input shaft and said output shaft having a common axisof rotation; a wet-plate clutch having first and second clutch memberscapable of rotating at different angular velocities, said wet-plateclutch configured for transferring torque between said first and secondclutch members when engaged, said first clutch member being connected tosaid input shaft; a pumping mechanism configured to engage said firstand second clutch members of said wet-plate clutch responsive to saidfirst and second clutch members rotating at different angularvelocities; a planetary set including first, second, third, and fourthelements organized about said common axis of rotation, said firstelement connected to said first clutch member and to said input shaft,said second element connected to said second clutch member, said thirdelement connected to said output shaft, and said fourth elementconnected between said first element and said second element, andbetween said second element and said third element; wherein said inputshaft, said wet-plate clutch, said second element, said third element,said fourth element, and said output shaft define a first torque paththrough said multi-path torque coupling; and wherein said input shaft,said first element, said third element, said fourth element, and saidoutput shaft define a second torque path through said multi-path torquecoupling.
 2. The torque coupling of claim 1 wherein said pumpingmechanism is a gear pump, said pumping mechanism including an externalgear coupled to said second clutch member and an internal gear coupledto said input shaft.
 3. The torque coupling of claim 1 wherein saidpumping mechanism includes an axial cam plate coupled to said secondclutch member and a piston pump disposed within a pump housing, saidpiston pump in operative relationship to said axial cam plate.
 4. Thetorque coupling of claim 1 wherein said first element is a ring elementlocated around said common axis; wherein said second element is a sunelement which rotates about said common axis; wherein said third elementis a carrier element which rotates about said common axis; and whereinsaid fourth element is a planetary element located between, and engagedwith, said sun and said ring elements, said planetary element disposedon said carrier element.
 5. The torque coupling of claim 1 wherein thepumping mechanism is a hydraulic pump self contained within the torquecoupling and configured to increase and decrease hydraulic pressureresponsive to an associated increase and decrease in the differencebetween the angular velocities of the first and second clutch members,wherein the transferred torque of the clutch is responsive to theincreased hydraulic pressure of the pumping mechanism.
 6. The torquecoupling of claim 1 further including a locking mechanism configured tomaximize torque transfer between said input shaft and said output shaft.7. The torque coupling of claim 6 wherein said locking mechanismconsists of a sprag controlled bi-directional clutch.
 8. The torquecoupling of claim 6 wherein said locking mechanism consists of a strutcontrolled bi-directional clutch.
 9. The torque coupling of claim 6wherein said locking mechanism is operatively disposed in parallel withsaid wet-plate clutch, between said first and second elements of saidplanetary set.
 10. The torque coupling of claim 6 wherein said lockingmechanism is operatively disposed between said first and third elementsof said planetary set.
 11. The torque coupling of claim 6 wherein saidlocking mechanism is operatively disposed between said second and thirdelements of said planetary set.
 12. The torque coupling of claim 6wherein said locking mechanism consists of a roller controlledbi-directional clutch.
 13. A torque coupling comprising: an input shaftadapted to be connected to a source of torque; an output shaft fromwhich torque is delivered; a clutch having first and second clutchmembers capable of rotating at different angular velocities, said clutchconfigured for transferring torque between said first and second clutchmembers when said first and second clutch members rotate at differentangular velocities, said first clutch member being connected to saidinput shaft; a locking mechanism configured to maximize torque transferbetween said input shaft and said output shaft; and a planetary setincluding first, second, third, and fourth elements organized about acommon axis of rotation, said first element connected to said firstclutch member and to said input shaft, said second element connected tosaid second clutch member, said third element connected to said outputshaft, and said fourth element connected between said first element andsaid second element, and between said second element and said thirdelement.
 14. The torque coupling of claim 13 wherein said lockingmechanism is further configured to lock said first element and saidthird element about said common axis of rotation.
 15. The torquecoupling of claim 13 wherein said locking mechanism is furtherconfigured to lock said second element and said third element about saidcommon axis of rotation.
 16. The torque coupling of claim 13 whereinsaid locking mechanism is further configured to lock said first elementand said second element about said common axis of rotation.
 17. In anautomotive vehicle having primary and secondary wheels, a power unitconnected directly to the primary wheels, and a torque couplingconnected between the power unit and the secondary wheels forapportioning torque between the primary and secondary wheels, saidtorque coupling comprising: a torque modulating clutch, a lockingmechanism independent of said torque modulating clutch, and a planetaryset connected such that a locking mechanical path and a separate torquemodulating clutch path exist through which torque is transferred betweenthe power unit and the secondary wheels, with the amount of torquetransferred through the torque modulating clutch path in relation to theamount transferred through the locking mechanical path being variable bythe torque modulating clutch, whereby the apportionment of torquebetween the primary and secondary wheels is controlled by the torquemodulating clutch and the independent locking mechanism.
 18. Amulti-path torque coupling for coupling an input shaft adapted to beconnected to a source of torque and an output shaft from which torque isdelivered wherein the input shaft and said output shaft having a commonaxis of rotation, the torque coupling comprising: a wet-plate clutchhaving first and second clutch members capable of rotating at differentangular velocities, said wet-plate clutch configured for transferringtorque between said first and second clutch members when engaged, saidfirst clutch member being connected to said input shaft; a pumpingmechanism configured to engage said first and second clutch members ofsaid wet-plate clutch responsive to said first and second clutch membersrotating at different angular velocities; a planetary set including aring gear, a sun gear, carrier, and a planet gear, each of which isorganized about the common axis of rotation, the ring gear is connectedto the first clutch member and to the input shaft, the sun gear isconnected to the second clutch member, the carrier is connected to theoutput shaft, the planet gear is connected between the ring gear and thesun gear and is also connected between the sun gear and the carrier,wherein the clutch, the sun gear, the planet gear and the carrier areconfigured for providing a first torque path between the input shaft andthe output shaft; and wherein the ring gear, the planet gear and thecarrier are configured for providing a second torque path between theinput shaft and the output shaft.
 19. The torque coupling of claim 18,further comprising a locking mechanism configured to maximize torquetransfer between said input shaft and said output shaft throughselectively bi-passing the first torque path and the clutch.
 20. Thetorque coupling of claim 19 wherein the locking mechanism is amechanical coupling of elements selected from the group consisting ofthe sun gear to the ring gear, the sun gear to the input shaft, thesecond clutch member to the ring gear, the second clutch member to theinput shaft, the carrier to the ring gear, the carrier to the inputshaft, the sun gear to the carrier, and the second clutch member to thecarrier.
 21. A multi-path torque coupling for coupling an input shaftadapted to be connected to a source of torque and an output shaft fromwhich torque is delivered wherein the input shaft and said output shafthaving a common axis of rotation, the torque coupling comprising: meansfor providing a mechanical clutch control responsive to an amplifieddifference between an angular velocity of the output shaft and anangular velocity of the input shaft; means for selectively transferringtorque between the input shaft and the output shaft responsive to theprovided clutch control; and means for providing a locking engagementfor mechanically transferring torque between the input shaft and theoutput shaft independent from the means for selectively transferring.